Study Of Fore-balanced Instantaneous Gas Water Heater's Combustion And Thermal Characteristics

Using the knowledge of combustion, heat transfer, fluid dynamics, orthogonal experiment and data processing theory, this paper gave a relatively detailed analysis on the combustion and thermal characteristics of fore-balanced instantaneous gas water heater, some author's standpoints were concluded and gave proposals on the heat enhancement of the instantaneous gas water heater.At first, by the theory knowledge and experimental data ,the author gave a detailed analysis on the heat transfer of fored-balanced instantaneous gas water heater, pointed out some characteristics of it and drew the following concludes: the heat exchange between fume and water takes place at two places—the combustion chamber and the heat exchanger. The conventional heat transfer between the fume and the wall of combustion chamber is the major one and it's ratio is about 30 percent, the radiation heat transfer between them is minor. Fume's flow in the heat exchanger is in low Reynolds number. The heat exchange coefficient of fume-side is low, whose average value varies little with the gas flow. The flow and heat exchange of water in the coil pipe is always in the entrance region whose heat exchange is greater than in the fully developed region, but it is very difficult to calculate the heat exchange coefficient between the water and the coil pipe precisely. For the heat exchanger, the heat exchanged in the first row of the coil pipe takes account about 65 percent, which is caused by the first row's different heat exchange mechanics from the others. With regard of the heat exchange enhancement, the author proposed that increase the distance between the fin tip and the first pipe properly, which is assisting of raise the Reynolds number of the flow, and transfer the round-shaped pipe to ellipse-shaped pipe. Through the orthogonal experiments, the author found out the major factor affecting the combustion and thermal characteristics from the gas pressure, water flow, air-inlet area and fume-exhaust area. The author used the regression analysis to get the relationship between the four factors listed above and the heat efficiency, oxygen's volume percentage in the fume, volume percentage of the CO in the fume and the fume temperature. The curves showing the relationship and analysis about them are given. The analysis showed that the extra air coefficient is an very important quality because it affects the heat efficiency, volume percent of the CO in the fume and the fumetemperature. Not any the combustion progress produces CO, the heat exchange between the water and the fume can also influence it's produce.